System and method for fixing a direction of magnetization of pinned layers in a magnetic field sensor

ABSTRACT

A spin valve GMR sensor configured in a bridge configuration is provided. The bridge includes two spin valve element pairs. The spin valve elements include a free layer, a space layer, a pinned layer, and a bias layer. The bias layer includes a first bias layer and a second bias layer. The first and second spin valve element pairs are formed on separate metal layers and a current pulse is applied to the metal layers, which sets the direction of magnetization in the pinned layer of the first pair of spin valve elements to be antiparallel to the direction of magnetization in the pinned layer of the second pair of spin valve elements. The same effect can be accomplished by making the pinned layer substantially thicker than the second bias layer in the first spin valve element pair and the pinned layer is substantially thinner than the second bias layer in the second spin valve element pair and applying a magnetic field to the first and the second spin valve element pairs.

FIELD

The present invention relates generally to giant magnetoresistive(“GMR”) sensors. More specifically, the present invention relates to aGMR sensor in which a direction of magnetization of pinned layers in theGMR sensor may be easily fixed.

BACKGROUND

The ability to sense and measure a magnetic field is important in manyareas. For example, magnetic sensors may be used for compassing,navigation, magnetic anomaly detection, and identifying position. As aresult, magnetic sensors may be found in medical, laboratory, andelectronic instruments; weather buoys; virtual reality systems; and avariety of other systems.

Such applications frequently employ magnetoresistive (“MR”) sensorscapable of sensing small magnetic fields. MR sensors are often formedusing integrated circuit fabrication techniques and are typicallycomposed of a nickel-iron (permalloy) thin film deposited on a siliconwafer, or other type of substrate, and patterned as resistive strips.The resistance of the strips varies with respect to an angle formedbetween a sensed magnetic field and current direction within the sensor.The strip resistance is maximized when the magnetic field and thecurrent direction are parallel to each other.

During the manufacture of an MR sensor, the easy axis (the preferreddirection of magnetization) is set to a direction along the length ofthe film to allow the maximum change in resistance of the strip.However, the influence of a strong magnetic could rotate themagnetization of the film, changing the sensor's characteristics.Following such changes, a strong restoring magnetic field can be appliedto the sensor to restore, or set, the sensor's characteristics.

In certain designs, large external magnets can be placed adjacent to thesensor to set the sensor's characteristics. However, such animplementation may not be feasible when the MR sensor has already beenpackaged into a system. Particularly, some applications require severalsensors within a single package to be magnetized in differentdirections. In such applications, instead of using large externalmagnets, individual coils may be wrapped around each sensor to restorethe sensor's characteristics. Alternatively, current straps, also knownas set-reset straps, may be used to restore the sensor'scharacteristics. The use of current straps in a magnetic field sensingdevice is discussed in U.S. Pat. No. 5,247,278 to Bharat B. Pant,assigned to the same assignee as the current application. U.S. Pat. No.5,247,278 is fully incorporated herein by reference.

Another type of magnetic sensor is a giant magnetoresistive (“GMR”)sensor. GMR sensors are typically employed in applications that requiremeasurements of relatively small magnetic fields. GMR sensors may bemanufactured using thin film technology and may include multiple layersof alternating ferromagnetic and non-magnetic materials. Generally, aGMR sensor includes two magnetic layers separated by a non-magneticlayer. The resistance of the magnetic layers is related to the directionof magnetization between the two magnetic layers.

Some of the structures currently being used to fabricate GMR elementsinclude unpinned sandwich, antiferromagnetic multilayer, spin valvestructures, and spin dependent tunnel structures.

The unpinned sandwich structure may include two magnetic layersseparated by a conducting non-magnetic layer. For example, an unpinnedsandwich structure may consist of two permalloy layers separated by alayer of copper.

An antiferromagnetic multilayer structure may consist of multiplerepetitions of alternating conducting magnetic layers and non-magneticlayers. In this structure, each magnetic layer may have a direction ofmagnetization antiparallel to the direction of magnetization of themagnetic layers on either side.

Spin valve structures may include a pinned magnetic layer and a freemagnetic layer, with a nonmagnetic layer, such as copper, locatedbetween the two magnetic layers. The pinned layer may have a fixedmagnetization direction, while the free layer may rotate in the presenceof an external magnetic field.

Spin dependent tunnel structures are similar to spin valve structures;however, the non-magnetic layer is a non-conductive material, such as anoxide, and current flows from one magnetic layer to another magneticlayer through a tunnel current in the non-conductive layer.

Magnetic field sensors using GMR elements are often fabricated in aWheatstone bridge configuration. A Wheatstone bridge can be fabricatedusing four GMR elements, such as spin valves. One of the biggestchallenges of fabricating a spin valve GMR sensor in a Wheatstone bridgeconfiguration is producing two GMR element pairs that responddifferently to the same external magnetic field. For a spin valve GMRsensor, the direction of magnetization of the pinned layers in adjacentlegs of the bridge should be antiparallel in order to utilize the GMRratio fully.

U.S. Pat. No. 5,617,071 entitled “Magnetoresistive structure comprisingferromagnetic thin films and intermediate alloy layer having magneticconcentrator and shielding permeable masses” discloses one approach tofix the direction of magnetization of the pinned layers in adjacent legsto be antiparallel by shielding one pair of Wheatstone bridge elements.By shielding opposing GMR elements with a highly permeable material, theshielded pair may not experience the effects of an applied magneticfield that rotates the direction of magnetization of the non-shieldedpair. However, this approach limits the range of the output signal,reduces sensitivity of the sensor in half, and requires extra processingsteps to fabricate the shielded layer.

U.S. Pat. No. 5,561,368 (hereinafter referred to as the '368 patent)entitled “Bridge Circuit Magnetic Field Sensor Having Spin ValveMagnetoresistive Elements Formed on Common Substrate” discloses anotherapproach for producing two GMR element pairs that respond differently tothe same external magnetic field. According to the '368 patent, four GMRspin valve elements are formed on the same substrate. The free layers ofall four of the spin valve elements have their magnetization axesparallel to one another. The pinned layers of two spin valve elementshave their magnetization axes antiparallel to the direction ofmagnetization of the pinned layers of the other two spin valve elements.

The magnetic field sensor in the '368 patent further includes anelectrically conductive fixing layer (a current strap) formed on thesubstrate. The application of current through the fixing conductorduring fabrication of the sensor fixes the direction of magnetization oftwo of the pinned layers to be antiparallel to the direction ofmagnetization of the other two pinned layers. While the current isapplied to the fixing conductor, the sensor is first heated and thencooled.

The application of the current during the sensor fabrication may bedifficult and not feasible, especially when many sensors are fabricatedon a single wafer. Multiple power supplies may be required to supply thecurrent to the fixing conductors or individual sensors may have to belinked. Thus, the methods described in the '368 patent may require acomplicated manufacturing process. Furthermore, applying heat during theprocess may reduce the GMR ratio for the material.

Therefore, a need exists for a simple method of setting themagnetization directions in the pinned layers of spin valve GMR sensorsconfigured in a Wheatstone bridge configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention is described below withreference to the drawings, in which:

FIG. 1 is a schematic diagram of a GMR sensor, according to an exemplaryembodiment;

FIG. 2 is a cross sectional view of a spin valve element, according toan exemplary embodiment;

FIG. 3 is a cross sectional view of a GMR sensor, according to anexemplary embodiment;

FIG. 4 is a cross sectional view of one half of a spin valve GMR sensorin a Wheatstone bridge configuration, according to an exemplaryembodiment;

FIG. 5 is a flow chart diagram of a method of fabricating a GMR sensor,according to an exemplary embodiment;

FIG. 6 is a cross sectional view of a GMR sensor, according to anexemplary embodiment; and

FIG. 7 is a flow chart diagram of a method of fabricating a GMR sensor,according to another exemplary embodiment.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram illustrating a giant magnetoresistive(“GMR”) sensor 100, according to an exemplary embodiment. The GMR sensor100 includes four spin valve elements 102, 104, 106, and 108 arranged ina bridge configuration, such as a Wheatstone bridge. Other bridgeconfigurations may be used. The GMR sensor 100 may be packaged as anintegrated circuit.

Spin valve elements 102-108 may be composed of GMR thin film layers asdescribed below with reference to FIG. 2. Spin valve element 102 mayrespond to an external magnetic field substantially in the same manneras spin valve element 106. Spin valve element 104 may respond to anexternal magnetic field substantially in the same manner as spin valve108.

Each of the spin valve elements 102-108 has a length and a width. Eachspin valve element 102-108 may be arranged so that each length isparallel to lengths of the other spin valve elements. Further, each spinvalve element 102-108 may be several hundred microns long and a fewmicrons wide. The width of each spin valve element 102-108 may varybased on the GMR sensor's sensitivity requirements, while the length ofeach element may vary based on the GMR sensor's resistance and sizerequirements.

The GMR sensor 100 may include four terminals 110, 112, 114, and 116. Asdepicted in FIG. 1, terminal 110 is located between spin valve elements102 and 108, terminal 112 is located between spin valve elements 102 and104, terminal 114 is located between spin valve elements 104 and 106,and terminal 116 is located between spin valve elements 106 and 108. Apower supply may be applied across terminals 110 and 114, which mayresult in an output of the bridge across terminals 112 and 116.Alternatively, the power supply may be applied across terminals 112 and116, resulting in an output of the bridge across the terminals 110 and114.

FIG. 2 is a cross sectional view of a spin valve element 200. Spin valveelement 200 may be substantially the same as spin valve elements 102-108depicted in FIG. 1. The spin valve element 200 may include a free layer202, a space layer 204, a pinned layer 206, and a bias layer 208. Asdepicted in FIG. 2, the pinned layer 206 is located substantially abovethe bias layer 208, the space layer 204 is located substantially abovethe pinned layer 206, and the free layer 202 is located substantiallyabove the space layer 204. The spin valve element 200 may includeadditional layers not shown in FIG. 2, such as a capping layer or abuffer layer.

The layers 202-208 of the spin valve element 200 may be deposited on asubstrate using standard semiconductor deposition processes. Forexample, the layers 202-208 may be deposited using sputtering. Thesubstrate may be composed of a semiconductor material such as silicon orgallium arsenide.

The layers 202-208 of the spin valve element 200 may be deposited in anexternal magnetic field. As a result, the free layer 202 and the pinnedlayer 206, which are both magnetic layers, may each possess a magneticeasy axis (a preferred direction of magnetization) due to their grainstructure. The easy axis of the free layer 202 may be substantiallyparallel to the length of the spin valve element 200. The easy axis ofthe pinned layer 206 may be substantially perpendicular to the length ofthe spin valve element 200.

The free layer 202 may be composed of a ferromagnetic material, such ascobalt, iron, nickel, and their related alloys. In a preferredembodiment, the free layer may be permalloy. However, otherferromagnetic materials may be used to form the free layer. The freelayer 202 may be free to rotate its direction of magnetization inresponse to an externally applied magnetic field.

The space layer 204 may be composed of a nonmagnetic material, such ascopper (Cu). However, other nonmagnetic materials may be used to formthe space layer. The space layer 204 may separate the two magneticlayers (e.g., the free layer 202 and the pinned layer 206). The spacelayer 204 may be thin enough so that the two magnetic layers 202, 206may be coupled. For example, the space layer 204 may be approximately1-4 nm. Accordingly, when one of the layers changes magneticorientation, the other magnetic layer may also change its orientation.

The pinned layer 206 may also be composed of a ferromagnetic material.While a layer composed of cobalt (Co) or a CoFe alloy is preferred forthe pinned layer, other ferromagnetic materials may be used. The biaslayer 208 may fix the magnetization direction of the pinned layer 206.Accordingly, when the pinned layer 206 is exposed to an externallyapplied magnetic field, the direction of magnetization of the pinnedlayer 206 may remain in its preferred or fixed orientation.

The bias layer 208 may be composed of an antiferromagnetic material. Thebias layer 208 may be composed of two layers, a first bias layer and asecond bias layer. In a preferred embodiment, the first bias layer maybe composed of ruthenium (Ru), while the second bias layer may becomposed of cobalt (Co). The first bias layer may be locatedsubstantially above the second bias layer. If the pinned layer 206 iscomposed of cobalt, the pinned layer 206 and the bias layer 208 may forma “sandwich” with the ruthenium layer located between the two cobaltlayers. The bias layer 208 may fix the magnetization direction of thepinned layer 206.

According to an exemplary embodiment, the thickness of the pinned layer206 and the thickness of the cobalt layer in the bias layer 208 may bedifferent. The thickness of the ruthenium layer in the bias layer 208may be selected so that it provides antiferromagnetic coupling betweenthe two adjacent cobalt layers. As a result the magnetizations of thesetwo cobalt layers have opposite directions. For example, the thicknessof the ruthenium layer may be approximately 4-7 Angstroms. In such anembodiment, the total magnetization from the two cobalt layers is verysmall, and thus, may not be easily influenced by an external magneticfield with low or moderate strength.

FIG. 3 is a cross-sectional view of a GMR sensor 300. FIG. 3 depictsspin valve elements 302, 304, 306, and 308 in a bridge arrangement,similar to the configuration depicted in FIG. 1. Spin valve elements302-308 are substantially the same as spin valve element 200 depicted inFIG. 2. In FIG. 3, the spin valve elements are shown with a free layerconsisting of permalloy, a space layer consisting of copper (Cu), apinned layer consisting of cobalt (Co), and a bias layer consisting of aruthenium/cobalt (Ru/Co) layer. However, the spin valve element layersmay be composed of different materials as discussed with reference toFIG. 2. FIG. 3 also depicts the direction of magnetization in each ofthe layers of the spin valve elements 302-308.

According to an exemplary embodiment, the direction of the magnetizationof the pinned layer in one of the spin valve elements is antiparallel tothe direction of the magnetization of the pinned layers in adjacent spinvalve elements (e.g., compare element 302 with elements 304 and 308).The arrows in the pinned layers represent the direction of themagnetization in these layers. The direction of magnetization in each ofthe pinned layers may be critical to the operation of the GMR sensor300. The layer of cobalt in the bias layer may have a magnetization in adirection opposite to that of the magnetization of the pinned layer ineach of the spin valve elements 302-308.

In the absence of a magnetic field, the direction of magnetization inthe free layers (permalloy layers) of each of the spin valve elements302-308 may be the same. As depicted in FIG. 3, the free layers have adirection of magnetization into the page, which is perpendicular to thedirection of the magnetizations in the two cobalt layers. Thisarrangement may provide the most linear response for the spin valveelements 302-308.

The bridge arrangement of the GMR sensor 300 may be balanced so that thespin valve elements 302-308 have equal resistance when not exposed to amagnetic field. If a voltage is applied across two opposite terminals ofa balanced GMR sensor 300 that is not exposed to an external magneticfield, the differential output across the two other terminals will equalzero.

However, when the balanced GMR sensor 300 is exposed to a magneticfield, the free layers may rotate while the pinned layers remain fixed,resulting in a change of resistance of each of the spin valve elements302-308. The resistance change may be proportional to the angle betweenthe magnetization direction of the fixed pinned layer and themagnetization direction of the rotating free layer. This change inresistance may be detected and the magnitude and polarity of the appliedmagnetic field may be determined from the resistance change.

One of the biggest challenges of manufacturing a spin valve GMR sensorin a Wheatstone bridge or similar configuration is fabricating thepinned layers to have antiparallel magnetic directions in adjacent legsof the bridge. In one embodiment, applying a current pulse to anisolated metal layer may be used to set the direction of magnetizationin the pinned layers.

FIG. 4 is a cross sectional view of one half of a Wheatstone bridgeconfiguration spin valve GMR sensor 400. It is understood that the GMRsensor 400 may have a second half substantially similar to the halfdepicted in FIG. 4. Spin valve elements 402 and 404 are substantiallythe same as spin valve elements 302 and 304 depicted in FIG. 3. Theconnections between spin valve elements 402 and 404 are not shown inFIG. 4 for the sake of simplicity, but it is understood that spin valveelement 402 is connected to spin valve element 404 in such a manner thatelement 402 is located adjacent to element 404 in a bridgeconfiguration. Accordingly, it is desirable for the direction of themagnetization in the pinned layer of spin valve element 402 to beantiparallel to the direction of the magnetization in the pinned layerof spin valve element 404.

Spin valve elements 402, 404 may be formed on dielectric layers 406,408. The dielectric layers 406, 408 may be deposited on metal layers410, 412. The metal layers 410, 412 may be deposited on a substrate.Standard semiconductor deposition processes may be used to deposit themetal layers 410, 412; the dielectric layers 406, 408; and the layers ofthe spin valve elements 402, 404.

The metal layers 410, 412 may be composed of copper, aluminum, or otherconducting material. The dielectric layers 406, 408 may be composed ofan insulating material, such as silicon dioxide or silicon nitride. Thesubstrate may be composed of a semiconductor material such as silicon orgallium arsenide.

The metal layers 410, 412 may be connected to electrodes or other deviceterminals. As such, a source may be applied to the metal layers 410, 412after device fabrication. For example, a current source may be appliedto the metal layers 410, 412. The metal layers 410, 412 may be connectedto the same current source, or each metal layer 410, 412 may beconnected to a different current source.

Metal layer 410 may be located on the same substrate as metal layer 412.However, metal layer 410 may be electrically isolated from metal layer412. Standard semiconductor isolation techniques may be used to providethe isolation. Accordingly, current flowing through metal layer 410 maynot impact metal layer 412, and vice versa.

After the GMR sensor has been fabricated, a current pulse may be appliedto each of the metal layers 410, 412. The current pulse may becharacterized as having a large peak and a short width. The peak of thecurrent pulse should be large enough to provide sufficient magneticfield to set the direction of magnetization in the spin valve elements402, 404, while the width should be short enough to avoid generating toomuch heat. For example, the current peak may range from 100 milliamperesto several amperes and the pulse may be approximately 1 microsecond.However, other current pulses with different peaks and widths may beused.

Applying a current pulse to each of the metal layers 410, 412 maygenerate a localized magnetic field. The magnetic field generated bycurrent flowing through metal layer 410 may affect spin valve element402, but not spin valve element 404. Likewise, the magnetic fieldgenerated by current flowing through metal layer 412 may affect spinvalve element 404, but not spin valve element 402.

The current flowing through metal layer 410 may be designed to flow in adirection opposite to that of the current flowing through metal layer412. The opposite directions of current flow through the metal layers410, 412 may generate the localized magnetic fields that cause spinvalve elements 402, 404 to orient in opposite directions. In response tothe pulse current, the layer of cobalt in the bias layer of spin valveelement 402 may be fixed in a direction antiparallel to the layer ofcobalt in the bias layer of spin valve element 404.

The current pulse may affect the total magnetization from the pinned andbiasing layers. The total magnetization may be the difference betweenthe magnetizations of the pinned and biasing layers because the momentsare in opposite directions. The total magnetization may align to themagnetic field direction generated by the current pulse.

FIG. 5 is a flow chart diagram of a method 500. The method 500 providesa method of fabricating a spin valve GMR sensor in a bridgeconfiguration, such as a Wheatstone bridge. Block 502 specifiesdepositing metal layers. The metal layers may be deposited onto asubstrate using standard semiconductor fabrication techniques. The metallayers may be composed of copper, aluminum, or other conductingmaterial. A separate metal layer may be deposited for each spin valveelement. Alternatively, a separate metal layer may be deposited for eachpair of spin valve elements having the same direction of magnetizationin their respective pinned layers. In yet another embodiment, a singlemetal layer may be deposited for all four spin valve elements in the GMRsensor.

Block 504 specifies depositing dielectric layers. The dielectric layersmay be composed of an insulating material, such as silicon dioxide orsilicon nitride. The dielectric layers may be deposited onto the metallayers using standard semiconductor fabrication techniques. Accordingly,there may be a separate dielectric layer for each spin valve element orfor each pair of spin valve elements having the same direction ofmagnetization in their respective pinned layers.

Block 506 specifies depositing spin valve element layers. The spin valveelement layers may include a free layer, a space layer, a pinned layer,and a bias layer. The spin valve element layers may be deposited ontothe dielectric layers using standard semiconductor fabricationtechniques. Four spin valve elements may be formed for each GMR sensorfabricated in a bridge configuration. The four spin valve elements maybe formed on separate dielectric layers. Alternatively, one pair of spinvalve elements may be formed on one dielectric layer and a second pairof spin valve elements may be formed on a second dielectric layer.

Block 508 specifies applying a current pulse to the metal layers. Thecurrent pulse may fix the direction of the magnetizations in the pinnedlayers to be in the same direction within each pair. Additionally, thecurrent pulse may fix the direction of the magnetizations of the pinnedlayers in one pair to be antiparallel to the magnetizations of thepinned layers in the other pair. The current pulse may be applied toelectrodes connected to the metal layers when the fabrication of the GMRsensor is substantially complete.

In an alternate embodiment, the spin valve elements may be depositedprior to depositing the dielectric layers and the metal layers. Thedielectric layers may be located substantially between the spin valveelement layers and the metal layers.

This method of making the pinned layers have antiparallel magneticdirections in the adjacent legs of a bridge may be advantageous becausethe current pulse is applied after the GMR sensor is fabricated.Applying a current to a current strap during fabrication may be verydifficult, especially when there are many sensors on a single wafer. Inaddition, by limiting the width of the current pulse, degradation of theGMR sensor due to heat may be avoided. The resulting bipolar GMR sensormay be highly sensitive to wide range of magnetic fields.

FIG. 6 is a cross sectional view of a GMR sensor 600. The GMR sensor 600includes two spin valve element pairs. Spin valve elements 602 and 606form the first pair, while spin valve elements 604 and 608 form thesecond pair. The first pair of spin valve elements may have a pinnedlayer (cobalt layer) that is substantially thicker than the layer ofcobalt in the bias layer. In contrast, the second pair of spin valveelements may have a pinned layer (cobalt layer) that is substantiallythinner than the layer of cobalt in the bias layer. For example, thecobalt layer thickness may be in the range of 3 to 20 nanometers.Additionally, the difference in thickness between the two cobalt layersmay be in the range of 0.4 to 10 nanometers. Other thicknesses may alsobe used.

The first spin valve element pair (spin valve elements 602 and 606) maybe formed on a substrate 610. Spin valve elements 602 and 606 may belocated diagonally in the bridge, such as spin valve elements 102 and106 in FIG. 1. Each spin valve element in the first spin valve elementpair may include a free layer, a space layer, a pinned layer, and a biaslayer. When the layers of the first spin valve element pair aredeposited, the pinned layer (cobalt layer) may be substantially thickerthan the layer of cobalt in the bias layer.

A first dielectric layer 612 may be deposited substantially around thetop and two sides of the first spin valve element pair, using standardsemiconductor deposition processes. The first dielectric layer 612 maybe composed of an insulating material, such as silicon dioxide orsilicon nitride.

A second dielectric layer 614 may be deposited on the substrate 610substantially adjacent to the first spin valve element pair. Thedielectric layer 614 may be composed of an insulating material, such assilicon dioxide or silicon nitride. Alternatively, the first dielectriclayer 612 may be deposited on the substrate 610 substantially adjacentto the first spin valve element pair, eliminating the need for thesecond dielectric layer 614. The second spin valve element pair (spinvalve elements 604 and 608) may be formed on the dielectric layer 614.Each spin valve element in the second spin valve element pair mayinclude a free layer, a space layer, a pinned layer, and a bias layer.When the layers of the second spin valve element pair are deposited, thepinned layer (cobalt layer) may be substantially thinner than the layerof cobalt in the bias layer.

After fabricating GMR sensor 600, the GMR sensor 600 may be magnetizedby a large external magnetic field. The magnetic field may be greaterthan 10 Gauss, depending on the film thickness. The magnetizations ofthe thicker layers of cobalt (e.g., the pinned layer of the first pairof spin valve elements and the layer of cobalt in the bias layer of thesecond pair of spin valve elements) may align in the same direction. Themagnetizations of the thicker layers of cobalt may be substantiallyaligned in the direction of the applied magnetic field.

Through the coupling of the layer of ruthenium (Ru) in the bias layer,the magnetizations of the thinner cobalt layers may align in a directionopposite to that of the thicker cobalt layers. As a result, theorientation of the magnetization of the pinned layers in the first spinvalve element pair may be antiparallel to the magnetization of thepinned layers in the second spin valve element pair.

FIG. 7 is a flow chart diagram of a method 700. The method 700 providesa method of fabricating a spin valve GMR sensor in a bridgeconfiguration. For example, the bridge configuration may be a Wheatstonebridge. Block 702 specifies forming a first spin valve element pair.Standard semiconductor deposition processes may be used to deposit thevarious layers of the two spin valve elements onto a substrate. Thelayers of the first spin valve element pair may be deposited such thatthe layer of cobalt in the bias layers are thinner than the pinnedlayers, which may also be composed of cobalt. A dielectric layer may bedeposited substantially around the top and two sides of the spin valveelement pair.

Block 704 specifies forming a second spin valve element pair. Adielectric layer may be deposited on the substrate substantiallyadjacent to the first spin valve element pair. Standard semiconductordeposition processes may be used to deposit the various layers of thetwo spin valve elements onto the dielectric layer located substantiallyadjacent to the first spin valve element pair. The layers of the secondspin valve element pair may be deposited such that the layer of cobaltin the bias layers are thicker than the pinned layers, which may also becomposed of cobalt.

Block 706 specifies applying a magnetic field. The magnetic field may beapplied to the first and second spin valve element pairs after they havebeen fabricated. The magnetic field may cause the magnetizations of thethicker layers of cobalt to align in the direction of the appliedmagnetic field. Through the coupling of the layer of ruthenium in thebias layer, the magnetizations of the thinner cobalt layers may align ina direction opposite to that of the thicker cobalt layers. As a result,the orientation of magnetization of the pinned layers in the first spinvalve element pair may be antiparallel to the magnetization of thepinned layers in the second spin valve element pair.

This method of making the pinned layers have antiparallel magneticdirections in adjacent legs of a bridge may be advantageous becausesimple fabrication methods are used. Because the applied magnetic fieldis applied to both spin valve element pairs, fabricating a shield layerfor half of the bridge may be unnecessary, which reduces the complexityof manufacturing the GMR sensor. The resulting bipolar GMR sensor may behighly sensitive to wide range of magnetic fields.

Methods 500 and 700 may also used for fabricating GMR sensors using spindependent tunnel elements. A difference between the spin valve elementsand a spin dependent tunnel element is the type of material used infabricating the space layer. While a space layer in a spin valve may becomposed of copper, the space layer in a spin dependent tunnel structuremay be composed of an oxide. A change in the type of spacer material maynot impact the effectiveness of the systems and methods described abovewith respect to a GMR sensor using spin valve elements.

It should be understood that the illustrated embodiments are exemplaryonly and should not be taken as limiting the scope of the presentinvention. The claims should not be read as limited to the describedorder or elements unless stated to that effect. Therefore, allembodiments that come within the scope and spirit of the followingclaims and equivalents thereto are claimed as the invention.

1-19. (canceled)
 20. A spin valve giant magnetoresistive sensor in abridge configuration, comprising in combination: a first pair of spinvalve elements in which each spin valve element contains at least a freelayer, a space layer, a pinned layer and a bias layer, wherein the biaslayer includes a first bias layer and a second bias layer, wherein thefirst bias layer is located substantially between the pinned layer andthe second bias layer, and wherein the pinned layer is substantiallythicker than the second bias layer; and a second pair of spin valveelements in which each spin valve element contains at least a freelayer, a space layer, a pinned layer, and a bias layer, wherein the biaslayer includes a first bias layer and a second bias layer, wherein thefirst bias layer is located substantially between the pinned layer andthe second bias layer, wherein the pinned layer is substantially thinnerthan the second bias layer, and wherein a direction of magnetization inthe pinned layer of the first pair of spin valve elements isantiparallel to a direction of magnetization in the pinned layer of thesecond pair of spin valve elements.
 21. The sensor of claim 20, whereinthe first spin valve element pair is formed on a substrate.
 22. Thesensor of claim 20, wherein a dielectric layer is depositedsubstantially around a top and two sides of the first spin valve elementpair.
 23. The sensor of claim 20, wherein the second spin valve elementpair is formed on a dielectric layer located substantially adjacent tothe first spin valve element pair.
 24. The sensor of claim 20, whereinthe pinned layer and the second bias layer are composed of cobalt. 25.The sensor of claim 20, wherein the first bias layer is composed ofruthenium.
 26. The sensor of claim 20, wherein the first bias layer isoperable to couple the pinned layer and the second bias layer.
 27. Thesensor of claim 20, wherein a magnetic field is applied to the firstspin valve element pair and the second spin valve element pair.
 28. Thesensor of claim 27, wherein the magnetic field is greater than 10 Gauss.29. The sensor of claim 27, wherein the magnetic field is operable toset a direction of magnetization in the pinned layer of the first pairof spin valve elements and the second bias layer of the second pair ofspin valve elements in a direction of the magnetic field.
 30. The sensorof claim 27, wherein the magnetic field is operable to set a directionof magnetization in the pinned layer of the second pair of spin valveelements and the second bias layer of the first pair of spin valveelements in a direction substantially opposite to that of the magneticfield.
 31. The sensor of claim 27, wherein the magnetic field isoperable to set a direction of magnetization in the pinned layer of thefirst pair of spin valve elements to be substantially antiparallel to adirection of magnetization in the pinned layer of the second pair ofspin valve elements.
 32. A method of fabricating a spin valve GMR sensorin a bridge configuration, comprising in combination: forming a firstspin valve element pair in which each spin valve element contains atleast a free layer, a space layer, a pinned layer and a bias layer,wherein the bias layer includes a first bias layer and a second biaslayer, wherein the first bias layer is located substantially between thepinned layer and the second bias layer, and wherein the pinned layer issubstantially thicker than the second bias layer; forming a second spinvalve element pair in which each spin valve element contains at least afree layer, a space layer, a pinned layer and a bias layer, wherein thebias layer includes a first bias layer and a second bias layer, whereinthe first bias layer is located substantially between the pinned layerand the second bias layer, and wherein the pinned layer is substantiallythinner than the second bias layer; and applying a magnetic field to thefirst spin valve element pair and the second spin valve element pair,thereby setting a direction of magnetization in the pinned layer of thefirst pair of spin valve elements that is substantially antiparallel toa direction of magnetization in the pinned layer of the second pair ofspin valve elements.
 33. The method of claim 32, wherein the pinnedlayer and the second bias layer are composed of cobalt.
 34. The methodof claim 32, wherein the first bias layer is composed of ruthenium. 35.The method of claim 32, wherein the first bias layer is operable tocouple the pinned layer and the second bias layer.
 36. The method ofclaim 32, wherein the magnetic field is greater than 10 Gauss.
 37. Themethod of claim 32, wherein the magnetic field is operable to set adirection of magnetization in the pinned layer of the first pair of spinvalve elements and the second bias layer of the second pair of spinvalve elements in a direction of the magnetic field.
 38. The method ofclaim 32, wherein the magnetic field is operable to set a direction ofmagnetization in the pinned layer of the second pair of spin valveelements and the second bias layer of the first pair of spin valveelements in a direction substantially opposite to that of the magneticfield.